[2] Added http status codes to template & example

These are not meant to cover all status codes, but the ones used for
the end-point. In the template, I have just added a few common ones
related to CRUD
#2 Added more commonly used status code
#2 Added commonly used status code to User example

This was copied directly from the Template.md file
#2 Invalid request 400, response added

Example added to Template & to User Example
#2 Renamed `Example` to `Methods`
#2 DELETE method added to template
#2 DELETE method added to User example
#2 Link added to User example
Merge pull request #7 from TransformCore/2-api-documentation

 [2] Added http status codes to template & example